VT super v6 fuel consumption

[whitedragoon]

Hello all,
I am new to holdens and recently bought 1998 VT wagon with supercharged engine in it. Pre-previous owner did some upgrades such as headers, 2.3 or 3in exhaust, coil packs, air intake, valve lifters and maybe some more. With a full tank im only can dobl 420km of 70% freeway and bit of the city driving.I tried to keep revs low as possible and not to boost supercharger but still no increase in fuel economy. Maybe someone could point me where i could start looking or maybe a place/person who could identify the problem. Can it be remaping ?

 

[devilly]

thanks for the pics makes it easier to help,from what i noticed is the header bolts are replacements not original.

this on mine caused a bit of and air leak.i had to change back to the originals bolts.

i also noticed that the o2 sensors looked a bit worn out on yours and when i put on my headers i waited a few months for the chemicals to burn off them and then had to change them out for new ones.

whats it doing at the exhaust pipe ? dripping fuel ? after a drive can you smell any raw fuel in the engine bay ?

 

[Immortality]

Yeah that is fairly terrible.

I'd start with the basics and do a full service, all fluids and all filters, plugs/leads etc Then on top of that, clean the MAF and add some injector cleaner. I would also consider enclosing that pod filter. As it is now under certain conditions it will be sucking hot air from in the bay and that will heat soak things more than usual and once you get cruising it takes ages to get all that heat out of the engine intake.

Depending on the mileage I would possibly consider new O2 sensors and injectors or get your injectors cleaned/reconditioned as they do gum up with age.

Also make sure you run 95ron fuel or better.

 

[whitedragoon]

devilly: no fuel smell or leaks noticed. Engine bay is surprisingly clean and exhaust too. Neither is smoking when you put your foot down. Car starts, idles and runs well without any suspisions Then only two things i noticed is that RPMS pulsates betweek 1k-1.2i when you coming of the throttle and start braking prior the stop. It actually sounds nice but unsure is it should be like that or not. And when parking on a hill engine idles around 500rpm or less but it clears up after short drive.

immortality: thank you for the advice, i will do basic servicing and see if it going to improve anything. Also run injector cleaner and will look at the maf. Does that aftermarket air filter gives anything at all? Personally it looks like showing off thing and thinking about putting back original box with k&n panel filter. And what are the thoughs about aftermarket O2 sensors?
Also thank you for fuel advice.All i could find so far was running 91 is good enough but now will have to change.
The car donr 200k kms but who knows what was the engine kms. Something was done to the top end for sure.
If i could get it like 550km prr full tank i think it would be reasonable?

 

[Immortality]

These engines are tuned for 95, run em on 91 and they will knock retard and run on the low ignition map

I suggest getting some Throttle Body cleaner and giving the TB a good clean, the idles issues are most likely related to the IAC passages been full of gunk that has built up over many miles of service.

I found the standard airbox to be a restriction, the best and cheapest mod is the MACE CAI, works and is functional and has the scope for further improvement down the line.

After market O2 sensors can be a bit hit and miss. Can get genuine Bosch/Delphi O2 sensors from ebay, 2 for about $90 + shipping so no need to cheap out there.

 

[whitedragoon]

Local mechanic/holden breaked mentioned that I am loosing all this fuel economy due to those aftermarket headers. Can it be true?

 

[Immortality]

I doubt it.

 

[Tree cutter]

I think most of your problem will be from running low octane fuel, but someone could have changed the diff ratio too so your engine is doing more revs on the highway. What revs are you doing at 100 Kph

 

[whitedragoon]

I think most of your problem will be from running low octane fuel, but someone could have changed the diff ratio too so your engine is doing more revs on the highway. What revs are you doing at 100 Kph

I think around 2000 rpm. Trying not to boos and keep it steady as possible.

 

[Immortality]

A gear swap shouldn't really effect fuel economy unless they have gone stupid with the ratio. I'm about to go to 3.73 gears and I'm not expecting to see any major change, yes the engine will be spinning a little faster but it's doing less work because it is easier to spin the rear wheels.